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Once you have solved the problem with your vehicle, make sure to use only pre-mixed antifreeze. The most common mix is 50% distilled water/50% antifreeze. Also, an antifreeze that meets Honda's specifications. If you mix it yourself, use either distilled, or RO water. But if you buy the pre-mixed one at the store, then you don't have to worry about it.
Older heating systems were designed to have a shutoff valve to stop the antifreeze flowing through the heater core inside the vehicle. This valve used to be located in the engine bay near the firewall. In this case one had to manually close the shutoff valve with a lever in the dashboard. But the vehicles now don't have the shutoff valve at the engine bay (maybe there are exceptions?). Anyway the vehicles I know of now, have an electronic mixing valve that regulate the amount of antifreeze that flows through the core. This valve is electronically linked to the heat/AC air vents, and can be a pain in the neck to work with.
The 2001 Silverado I have has one of these "environmental controls" with an electric motor that regulates the air flow (defrost vents, floor vents, and so on). This motor (at the driver's side under the dash) is linked to another motor (at the passenger side under the dash) that controls either hot or cold air temperatures. Turn to control to Hot and the motor turns a small door to allow hot air to flow. Turn the level to cold or AC, and the motor turns the panel the other way.
If your coolant is hot enough and you don't have hot air blowing, then the heater core is not getting the coolant. So it could be clogged, have a collapsed hose, or the valve malfunctioning.
You need a better mechanic I think.
Bring your car to a mechanic who actually knows how to fix things, your current one is clueless. Heater core and blend door are captain obvious things. Was the first two thermostats shot, especially the 1st new one you put in? Why would you put a third one in?
Step #1 for me is to plug in a OBD2 scanner than does live data, and pull up the coolant temp reading. Is the coolant temp getting up to 190-210 degrees?
Identify the heater hoses going into the firewall. Are they hot to the touch with the engine warmed up? Can you feel both hoses are about the same temp (return hose might be a tad cooler).
It could also be a blend door issue. The blend door is what regulates the heated air from the heater core and the cooled air from the A/C. Some of these are cable actuated and some are electronic. It's possible the blend door motor has failed (or the cable has snapped) and the door is stuck on the cooler side of things.
Screw the reader for this.. Just look at the temp gauge.. is it in the 'normal' position? that gauge is getting the data from the ECU, which is the same thing you'd get from the reader.
Don't get me wrong.. I think it's great to have a reader.. But.. Getting one just to read the temp? Meh. The gauge won't be as accurate, but it'll be fine for this. If the sensor were out, the reader wouldn't do you any good. Well, other than a code that says the sensor is out. In which case.. MIL would be set.
Good call on the blend door. Most of them are electric now.. If the blend door isn't working properly, either due to mechanical or electrical issues.. NOW a code reader might be useful.. I don't know if it would report an issue from the HVAC module or not.. Certainly wouldn't set the MIL/SES, but a blend door issue should set a code in any vehicle from.. 2015 forward, at least. Just a matter of whether a 'basic' reader would pull that code. Just noticed this is before 2015.. So.. Questionable.
FWIW.. have your mechanic pack up his parts cannon and send him on his way. If the thermostat was stuck (or sticking) open, THAT would have set a code and turned on the MIL.. P0128 IIRC, unless it was intermittent, in which case, there'd STILL be a pending P0128 stored.. And any mechanic that says "Huh.. Let's try replacing that new factory part with an aftermarket one" needs to be whacked upside the head. Thermostat isn't that big a deal, but you try that on some sensors.. O2 especially.. You're begging for headaches.
All this being said.. my money is on the heater core. And, since it's not leaking, a flush of it with some CLR could do wonders. I've never done that method myself as. I've never actually had a bad heater core (knock on wood).. One thing I'm not clear on.. OP doesn't CLEARLY mention whether air is blowing normally and it's just not hot, though that's my assumption.. or if there's restricted airflow.. in which case.. the old Cabin Air Filter would be the prime suspect.
find out were the heater core hoses come out of the firewall, feel the hoses, the temperature should be similiar in both hoses. if one hose is hot, the other is cool. blocked heater core.
I have a Honda Civic 8th gen 2006 - 2011 and my heater is not working properly. I am honestly just fed up at this point, I feel like my heater will never go back blowing hot air like before! These are things that my mechanic has done! (Im blowing a lot of money on parts!)
I changed the thermostat (First time)
I burped the system and put the car on a incline on a lift
I changed the thermostat again (This time with a aftermarket one)
Burped the system at a incline with the lift
When he changed the thermostat last he made run the engine and than feel the bottom hose saying its nice and hot now (after reving for about 1 min). Today again same issue! My car heater just does not get hot like it used to anymore! At idle the car goes from halfway point to 4 or 5 bars and the heat obv is not as hot only when I start driving the engine temp goes back to the middle and the heat gets hotter. I told my mechanic this and he told me its normal and just to rev the engine or recirculate the heat to make the car hot. Its -5C (23F) outside. MY CAR NEVER DID THIS BEFORE! NEVER! I used to turn on the heat even on the highway at full fan speed and my legs would be burning sometimes! Now its changed..
I honestly don't know what to do! I have no idea what it is.
Is my mechanic right? Is it just normal for a car to do that?
When it comes to the heater or radiator in a vehicle the first thing that comes to mind is safety first. Never work on or check a cooling system when it is hot. Check coolant levels after the system has cooled over night. Engine cooling and passenger compartment heating use the same water antifreeze mix described as coolant in the owners manual. The engine coolant side simply cools the engine with the mixture described above circulating in a loop between the engine and the radiator pushed by a water pump which is normally driven by a belt, gear on the engine or an electric pump on some newer models.
Regulating the cooling process is the fan that is attached to the radiator and the thermostat located on the engine. The thermostat precisely controls temperature and allows water/antifreeze mixture to flow through the engine and back to the radiator where excess heat in the coolant is dispelled thru the radiator and the process begins again at the thermostat. The thermostat is an automatic valve that opens and closes due to the explanation and contraction caused by engine combustion heat or the release of engine heat by the radiator with the help of air flow while the vehicle is moving or it's fan or fans while at stop lights and or idling.
With the above cooling circuit there are a number of controls which keep the temperature gauge in the same place winter or summer while driving at low speed or high speed in a properly maintained engine cooling system. In addition to the thermostat automation, the radiator electric fans or thermostatically controlled clutch also have sensors or mechanisms which turn them on and off when the coolant in the system rises above a given temperature. The heater circuit explanation is coming, but you must understand engine cooling before we are able to explain the passenger heating system.
Next You have the coolant reservoir tank which has to be filled to it's full mark with the recommended coolant as outlined in the owners manual. Again never check the radiator or unless the system is cold and has been shut off over night. The coolant tank on my car is 20 years old and I can not see thru the old plastic so I make a dipstick out of a twisted paper towel and I'm able to twist the towel into the tank and get an existing level and add coolant from there as necessary.
Next the radiator cap is a very important part in the system (again don't touch it if the system hasn't cooled over night.) The radiator cap works of both pressure and vacuum. In other words when the cap is working properly the radiator cap will allow the coolant in the reserve tank to be drawn back into the engine coolant loop via vacuum and fill the system and keep to filled. Think straw and milk shake and you see now how the system automatically refills itself.
Next the pressure side of the radiator cap allows the radiator to purge excess coolant in the engine side of system back to the expansion tank when necessary as the system heats up. The radiator cap as you can see is an important part of the process that opens and closes via system pressure and vacuum to maintain the coolant pressure and level that it is also designed to contain.
Now another word about the thermostat which is another valve mentioned earlier. The thermostat is specific and designed to work at specific temperatures, example as in fully open at 194 degrees f and fully closed at 180 degrees f. The thermostat spends it's working hours while the engine is running opening and closing as engine and outside temperatures make demands. If the system is full of the correct coolant and the correct thermostat has been installed correctly (hint the hole in the thermostat being installed right side up is sometimes overlooked) and the water pump is pumping coolant around the circuit than You Should See The Radiator And Coolant Reservoir Tank Both Full when the system is cool.
That is 90% of what has to happen for your cabin heat to work.
Next your cabin fan has to work and you can test the system by directing the air via the controls to the windshield defrost position, upper dash vents lower dash vents. Go thru the same process checking vent outlets and this time use the fan speed controls to check high, medium, low air flow.
From there either check your cabin filter if have not changed it. I do it yearly on my car. Next have a look between the windshield and the hood and clean any leaves and or other trash which may have accumulated in that area.
Next you should have a fresh air indicator button on the dash which either allows fresh air to come into your cabin from outside or to allow the existing cabin air to recirculate within the cabin. I mostly let air in the cabin recirculate as to not fill your car with the exhaust of the vehicles in front of you.
Last if you have been able to fill the reservoir tank and get results, remember that it is your responsibility to keep it full in the future even you pay someone to do service on your car, because the system could develop a problem in the future and you will be the first to know with your new knowledge and head off problems in the future.
Hello everyone thank you for the answers, I have decided to switch my mechanic as he may be incompetent.. I told him the heat was STILL NOT WORKING, and his answer was lets replace the thermostat AGAIN(3rd time) and he wanted me to pay again! I said screw it and decided to bring it to another mechanic.
After reading everyone answers on it being the heater core, I am more inclined to explain to the next mechanic to please check there and that my thermostat has been changed already.
Question though, the aftermarket thermostat I have installed, should I switch that out and buy another OEM Honda one, is it bad to keep the aftermarket thermostat in my civic?
Last edited by Whale12; 01-19-2024 at 05:53 AM..
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heater core
